Node.js Stream 可写. end()方法
原文:https://www . geesforgeks . org/node-js-stream-written-end-method/
可写. end()方法是 Stream 模块的内置应用编程接口，这样就不会再有数据写入可写了。参数块和编码是可选的，这将允许在关闭流之前立即写入最后一个新的数据块。此外，可选的回调函数被添加为可写流的“完成”事件的监听器。
语法:
writable.end( chunk, encoding, callback)
参数:该方法接受三个参数，如上所述，如下所述:
- Chunk: is an optional data writing. The value of the block must be a string, buffer or Uint 8 array. For object mode, the block value can be any value other than null.
- Code: If the chunk is a string value, the code value is saved.
- Callback: is an optional callback function of the stream.
返回值:它返回调用此方法之前写入的数据，如果 end()方法有一大块新数据，那么它也会在末尾返回。
下面的例子说明了在 Node.js 中可写. end()方法的使用:
例 1:
// Node.js program to demonstrate the
// writable.end() method
// INcluding stream module
const stream = require('stream');
// Creating a stream and creating
// a write function
const writable = new stream.Writable({
// Write function with its
// parameters
write: function(chunk, encoding, next) {
// Converting the chunk of
// data to string
console.log(chunk.toString());
next();
}
});
// Writing data
writable.write('hi');
// Calling end method with its
// all the parameters
writable.end("last data", "utf8", () => {
console.log("Writable stream ended!");
});
输出:
hi
last data
Writable {
_writableState:
WritableState {
objectMode: false,
highWaterMark: 16384,
finalCalled: false,
needDrain: false,
ending: true,
ended: true,
finished: false,
destroyed: false,
decodeStrings: true,
defaultEncoding: 'utf8',
length: 0,
writing: false,
corked: 0,
sync: false,
bufferProcessing: false,
onwrite: [Function: bound onwrite],
writecb: null,
writelen: 0,
bufferedRequest: null,
lastBufferedRequest: null,
pendingcb: 2,
prefinished: true,
errorEmitted: false,
emitClose: true,
autoDestroy: false,
bufferedRequestCount: 0,
corkedRequestsFree:
{ next: null,
entry: null,
finish: [Function: bound onCorkedFinish] } },
writable: false,
_write: [Function: write],
domain: null,
_events:
[Object: null prototype] {
finish: { [Function: bound onceWrapper] listener: [Function] } },
_eventsCount: 1,
_maxListeners: undefined }
Writable stream ended!
例 2:
// Node.js program to demonstrate the
// writable.end() method
// INcluding stream module
const stream = require('stream');
// Creating a stream and creating
// a write function
const writable = new stream.Writable({
// Write function with its
// parameters
write: function(chunk, encoding, next) {
// Converting the chunk of
// data to string
console.log(chunk.toString());
next();
}
});
// Writing data
writable.write('hi');
// Calling end method with its
// all the parameters
writable.end("last data", "utf8", () => {
console.log("Writable stream ended!");
});
writable.write('GfG');
输出:
hi
last data
Error [ERR_STREAM_WRITE_AFTER_END]: write after end
at writeAfterEnd (_stream_writable.js:248:12)
at Writable.write (_stream_writable.js:296:5)
at /home/runner/LuxuriousLegitimateObservation/index.js:30:10
at Script.runInContext (vm.js:133:20)
at Object. (/run_dir/interp.js:156:20)
at Module._compile (internal/modules/cjs/loader.js:778:30)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
at Module.load (internal/modules/cjs/loader.js:653:32)
at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
at Function.Module._load (internal/modules/cjs/loader.js:585:3)Writab
le stream ended!
这里显示一个错误，因为在 end()方法之后调用 write()方法是不可能的。
参考:https://nodejs . org/API/stream . html # stream _ written _ end _ chunk _ encoding _ callback
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